Mobile Computing IEEE Standard 9/10/14. CSE 40814/60814 Fall 2014

Transcription

1 Mobile Compuing CSE 40814/60814 Fall 2014 IEEE IEEE (Ins4ue of Elecrical and Elecronics Engineers) esablished he Group in Specifica4ons for sandard ra4fied in Ini4al speeds were 1 and 2 Mbps. IEEE modified he sandard in 1999 o include: b a g was added in IEEE creaed sandard, bu Wi- Fi Alliance cer4fies producs Sandard is primarily concerned wih he lower layers of he OSI model. Daa Link Layer Logical Link Conrol (LLC). Medium Access Conrol (MAC). Physical Layer Physical Layer Convergence Procedure (PLCP). Physical Medium Dependen (PMD). 1

2 IEEE Sandards Local wireless neworks WLAN Personal wireless nes WPAN WiFi a b ZigBee Blueooh Wireless disribu4on neworks WMAN (Broadband Wireless Access) + Mobiliy h i/e/ /n/ /z g a/b/c/d/e ,.6 (WBAN) WiMAX [ (Mobile Broadband Wireless Access)] e (addi4on o.16 for mobile devices) b/c Wi-Fi Alliance Mission Saemen Non- profi organiza4on Cer4fy he ineroperabiliy of producs and services based on IEEE echnology Grow he global marke for Wi- Fi CERTIFIED producs and services across all marke segmens, plaaorms, and applica4ons Rigorous ineroperabiliy es4ng requiremens New Cerificae & Logo Cerificae inside packaging (opional) Logo on produc packaging (mandaory) Helps reailers and consumers 2

3 Wi-Fi Sandards Con b: Typical Daa Rae 6Mbi/s Max Daa Rae 11Mbi/s Range Indoor Approx. 100 Fee Range Oudoor Approx. 300 Fee b Sandard Well- suppored, sable, and cos effec4ve, bu runs in he 2.4 GHz range ha makes i prone o inerference from oher devices (microwave ovens, cordless phones, ec) and also has securiy disadvanages. Limis he number of access poins in range of each oher o hree. Has 11 channels, wih 3 non- overlapping, and suppors raes from 1 o 11 Mbps, bu realis4cally abou 4-5 Mbps max. Channel selecion (non-overlapping) Europe (ETSI) channel 1 channel 7 channel MHz [MHz] US (FCC)/Canada (IC) channel 1 channel 6 channel MHz [MHz] 3

4 Wi-Fi Sandards a: Typical Daa Rae 25Mbi/s Max Daa Rae 54Mbi/s Range Indoor Approx. 75 Fee Range Oudoor Approx. 225 Fee a Sandard Compleely differen from 11b and 11g. Flexible because mul4ple channels can be combined for faser hroughpu and more access poins can be co- locaed. Shorer range han 11b and 11g. Runs in he 5 GHz range, so less inerference from oher devices. Has 12 channels, 8 non- overlapping, and suppors raes from 6 o 54 Mbps, bu realis4cally abou 27 Mbps max Uses frequency division mul4plexing 4

5 OFDM in IEEE a OFDM wih 52 used subcarriers (64 in oal) 48 daa + 4 pilo (plus 12 virual subcarriers) khz spacing pilo khz channel cener frequency subcarrier number Wi-Fi Sandards Con g: Typical Daa Rae 25Mbi/s Max Daa Rae 54Mbi/s Range Indoor Approx. 75 Fee Range Oudoor Approx. 225 Fee g Sandard Exension of b, wih he same disadvanages (securiy and inerference). Has a shorer range han b. Is backwards compa4ble wih b so i allows or a smooh ransi4on from 11b o 11g. Flexible because mul4ple channels can be combined for faser hroughpu, bu limied o one access poin. Runs a 54 Mbps, bu realis4cally abou Mbps and abou 14 Mbps when b associaed Uses frequency division mul4plexing 5

6 Wi-Fi Sandards Con n: Typical Daa Rae 200Mbi/s Max Daa Rae 540Mbi/s Range Indoor Approx. 150 Fee Range Oudoor Approx. 375 Fee Infrasrucure vs. Ad-Hoc Neworks infrasrucure nework AP AP wired nework AP: Access Poin AP ad- hoc nework Archiecure of an Infrasrucure Nework STA 1 ESS BSS LAN Access Poin BSS 2 Disribu4on Sysem Access Poin 802.x LAN Poral Sa4on (STA) erminal wih access mechanisms o he wireless medium and radio conac o he access poin Basic Service Se (BSS) group of sa4ons using he same radio frequency Access Poin sa4on inegraed ino he wireless LAN and he disribu4on sysem Poral bridge o oher (wired) neworks Disribu4on Sysem inerconnec4on nework o form one logical nework (ESS: Exended Service Se) based on several BSS STA LAN STA 3 6

7 Archiecure of an Ad-Hoc Nework STA 1 IBSS LAN STA 2 STA 3 Direc communica4on wihin a limied range Sa4on (STA): erminal wih access mechanisms o he wireless medium Independen Basic Service Se (IBSS): group of sa4ons using he same radio frequency IBSS 2 STA 5 STA LAN Infrasrucure nework There is an Access Poin (AP), which becomes he hub of a sar opology. Any communicaion has o go hrough AP. If a Mobile Saion (MS, STA), like a compuer, a PDA, or a phone, wans o communicae wih anoher MS, i needs o send he informaion o AP firs, hen AP sends i o he desinaion MS Muliple APs can be conneced ogeher and handle a large number of cliens. Used by he majoriy of WLANs in homes and businesses. Roaming In an exended service area, a mobile saion (MS) can roam from one BSS (Basic Service Se) o anoher. Roughly speaking, he MS keeps checking he beacon signal sen by each AP and selec he sronges one and connec o ha AP. If he BSSs overlap, he connecion will no be inerruped when an MS moves from one se o anoher. If no, he service will be inerruped. Two BSSs coverage areas can largely overlap o increase he capaciy for a paricular area. If so, he wo access poins will use differen channels. 7

8 MAC Layer I - DFWMAC Traffic services Asynchronous Daa Service (mandaory) exchange of daa packes based on bes- effor suppor of broadcas and mul4cas Time- Bounded Service (op4onal) implemened using PCF (Poin Coordina4on Func4on) Access mehods DFWMAC- DCF CSMA/CA (mandaory) collision avoidance via randomized back- off mechanism minimum disance beween consecu4ve packes ACK packe for acknowledgemens (no for broadcass) DFWMAC- DCF w/ RTS/CTS (op4onal) Disribued Founda4on Wireless MAC avoids hidden erminal problem DFWMAC- PCF (op4onal) access poin polls erminals according o a lis MAC Layer II Priori4es defined hrough differen iner frame spaces no guaraneed, hard priori4es (Shor Iner Frame Spacing) highes prioriy, for ACK, CTS, polling response PIFS (PCF IFS) medium prioriy, for 4me- bounded service using PCF (DCF, Disribued Coordina4on Func4on IFS) lowes prioriy, for asynchronous daa service medium busy PIFS conen4on nex frame direc access if medium is free CSMA/CA Access Mehod I Sa4on ready o send sars sensing he medium (Carrier Sense based on CCA, Clear Channel Assessmen) If he medium is free for he dura4on of an Iner- Frame Space (IFS), he sa4on can sar sending (IFS depends on service ype) If he medium is busy, he sa4on has o wai for a free IFS, hen he sa4on mus addi4onally wai a random back- off 4me (collision avoidance, mul4ple of slo- 4me) If anoher sa4on occupies he medium during he back- off 4me of he sa4on, he back- off 4mer sops (fairness) conen4on window (randomized back- off mechanism) medium busy direc access if medium is free nex frame slo 4me (20µs) 8

9 Compeing Saions bo e bo r bo e bo r bo e busy sa4on 1 bo e busy sa4on 2 sa4on 3 busy bo e busy bo e bo r sa4on 4 bo e bo r bo e busy bo e bo r sa4on 5 busy medium no idle (frame, ack ec.) packe arrival a MAC bo e elapsed backoff 4me bo r residual backoff 4me CSMA/CA Access Mehod II Sending unicas packes sa4on has o wai for before sending daa receivers acknowledge a once (aoer wai4ng for ) if he packe was received correcly (CRC) auoma4c reransmission of daa packes in case of ransmission errors sender receiver oher sa4ons daa wai4ng 4me ACK conen4on daa DFWMAC Sending unicas packes sa4on can send RTS wih reserva4on parameer aoer wai4ng for (reserva4on deermines amoun of 4me he daa packe needs he medium) acknowledgemen via CTS aoer by receiver (if ready o receive) sender can now send daa a once, acknowledgemen via ACK oher sa4ons sore medium reserva4ons disribued via RTS and CTS sender receiver RTS CTS daa ACK oher sa4ons NAV (RTS) NAV (CTS) defer access conen4on daa 9

10 Fragmenaion sender receiver RTS CTS frag 1 ACK 1 frag 2 ACK 2 oher sa4ons NAV (RTS) NAV (CTS) NAV (frag 1 ) NAV (ACK 1 ) conen4on daa Frame Forma Types conrol frames, managemen frames, daa frames Sequence numbers imporan agains duplicaed frames due o los ACKs Addresses receiver, ransmiqer (physical), BSS iden4fier, sender (logical) Miscellaneous sending 4me, checksum, frame conrol, daa byes Frame Dura4on/ Address Address Address Sequence Address Daa CRC Conrol ID Conrol 4 bis Proocol version Type Subype To DS From More DS Frag Rery Power More WEP Mgm Daa Order MAC address forma scenario o DS from address 1 address 2 address 3 address 4 DS ad-hoc nework 0 0 DA SA BSSID - infrasrucure 0 1 DA BSSID SA - nework, from AP infrasrucure 1 0 BSSID SA DA - nework, o AP infrasrucure nework, wihin DS 1 1 RA TA DA SA DS: Disribu4on Sysem AP: Access Poin DA: Des4na4on Address SA: Source Address BSSID: Basic Service Se Iden4fier RA: Receiver Address TA: Transmiqer Address 10

11 Special Frames: ACK, RTS, CTS Acknowledgemen ACK Reques To Send RTS byes Frame Receiver Dura4on CRC Conrol Address byes Frame Receiver Transmiqer Dura4on CRC Conrol Address Address Clear To Send CTS byes Frame Receiver Dura4on CRC Conrol Address MAC managemen Synchroniza4on ry o find a LAN, ry o say wihin a LAN synchroniza4on of inernal clocks, genera4on of beacons Power managemen sleep- mode wihou missing a message periodic sleep, frame buffering, raffic measuremens Associa4on/Reassocia4on inegra4on ino a LAN roaming, i.e., change neworks by changing access poins scanning, i.e., ac4ve search for a nework MIB - Managemen Informa4on Base managing, read, wrie Synchronizaion using a Beacon (infrasrucure) beacon inerval (20ms 1s) access poin medium B B B B busy busy busy busy value of he 4mesamp B beacon frame 11

12 Synchronizaion using a Beacon (adhoc) beacon inerval sa4on 1 B 1 B 1 sa4on 2 medium B 2 B 2 busy busy busy busy value of he 4mesamp B beacon frame random delay 12